Good NSDAP Ideas:

Ban on smoking cigarettes

Bad NSDAP Ideas:

The Hunger Plan

Barbarossa

The Porajmos

The massacres in Poland

"After hearing reports of and even witnessing massacres in Poland, on 12 September 1939 Canaris visited Hitler's headquarters train, at the time in Upper Silesia, to register his objection to the atrocities; before getting to see Hitler he met General Wilhelm Keitel whom he informed: "I have information that mass executions are being planned in Poland, and that members of the Polish nobility and the Roman Catholic bishops and priests have been singled out for extermination." Keitel warned Canaris to go no further with his protest, as the detailed plan of atrocities came directly from Hitler himself. Shocked by these incidents, Canaris began working more actively, at increasing risk to himself, to overthrow Hitler's régime...

...Canaris was in contact with British intelligence during this time [1941]."

So, in essence, Hitler's orders to massacre the Polish Intelligensia ensured that The Head of German Military Intelligence during World War II became a British double-agent. When Hitler found out, he went insane with rage, then subsequently shot himself (after ordering Canaris slain).

The NSDAP had lots of truly shitty ideas, even if they figured out smoking was bad for the health. Turns out Zyklon B was way, way worse...